Chapter 6 Applied Instruction The PLC sends the data. CRC CHK (01) above is the error checking code. It can be calculated by means of the instruction CRC. (8-bit mode: SM606 is ON.) CRC check code: 16#02 is stored in the low 8-bit in D106, and 16#07 is stored in the low 8-bit in D107. Additional remark: 1. The format of the communication data in the RTU mode: 2. CRC check code: The check code starts from the address to the data. The operation rule is as follows. Step 1: Suppose the data in the 16-bit register (the register in which the CRC check code is stored) is 16#FFFF. Step 2:
The logical operator XOR takes the first 8-bit message and the low 8-bit data in the 16-bit register, and performs the logical exclusive OR operation on each pair of corresponding bits. The operation result is stored in the 16-bit register. Step 3: The values of the bits in the 16-bit registers are shifted by one bit to the right. The value of the highest bit becomes 0. 6-415 Register Data Description D100 Low 8 bits 16#01 Address D101 Low 8 bits 16#06 Function D102 Low 8 bits 16#20 Data address D103 Low 8 bits 16#00 D104 Low 8 bits 16#00 Data D105 Low 8 bits 16#12 D106 Low 8 bits 16#02 CRC CHK 0 D107 Low 8 bits 16#07 CRC CHK 1 START Time interval Address Communication address:
8-bit binary address Function Function code: 8-bit binary code DATA (n-1) Data: n×8-bit data ……. DATA 0 CRC CHK Low CRC check code: The 16-bit check code is composed of two 8-bit binary codes. CRC CHK High END Time interval